One important physical difference between humans and apes concerns human hair's ability to grow ceaselessly. And people make great fuss about their head adornment, as hair can be a sign of good health. Sometimes, this can turn a little bit ridiculous, like in this case: the hair is longer than the owner.
Xia Aifeng, 36, a Chinese woman from Shangrao, in eastern China's Jiangxi province, has not cut her hair for 16 years, since she was 20. Her hair has grown to 2.42 meters (8 ft) long, while she is just 1.6 m tall!
Xia washes her tresses once a week, a process which takes 90 minutes. The genetics of this woman is amazing, as hair has a three-stage development: growth (anagen), degeneration (catagen) and rest (telogen).
There are about 100,000 to 150,000 hair follicles on the scalp.
The anagen phase leads to the rapid multiplication of cells from the follicle's base (bulb), resulting in the continuous growth of hair fiber. When anagen ends, the hair-producing cells starts dying, entering the catagen phase, which lasts for a few weeks. After that, the telogen installs, when the follicle is metabolically inert and it can last for several weeks to even months. After that, the follicle enters another cycle: a new anagen and a new hair fiber start growing. The new fiber pushes out the old fiber which then falls out, often while brushing your hair.
As the cycles of the different follicles do not coincide, different parts of the body produce hairs of different lengths, depending on the various anagen time periods.
Scalp follicles can stay in anagen for many years, producing fibers over one meter in length, while the body hair remains in anagen only weeks or months, generating shorter hair. Xia's anagen could be really long...